1. Field of the Invention
The present invention relates to a structure improving the light utilization rate of LCDs (Liquid Crystal Displays), and in particular to a structure for reducing the diffraction effect in periodic electrode arrangements and liquid crystal devices including the same. Transparent dielectric layers having different diffraction indices are formed between periodic electrodes and thickness of each transparent dielectric layer is adjusted so that optical paths of the incident lights at the passivation layers and the transparent electrodes are equal. Light collection efficiency is thus improved.
2. Description of the Related Art
The display of light and dark on a thin film transistor liquid crystal display (TFT-LCD) is obtained by rotating the polarization direction of light, and by the birefringence characteristic of the liquid crystal. The main drawback of LCDs, when compared with self-illuminating displays, is narrow viewing angle, due mainly to do with the angle of incident light. Different viewing angles produce different display qualities, and the greater the viewing angle, the lower the contrast between viewing angles.
Recently, lateral electric field has been applied as a method for improving viewing angle, contrast and response in LCDs. Lateral electric field is produced by arranging the direction of the electric field and the liquid crystal molecules on the same plane to drive the liquid crystal molecules. Phase differences caused by incident light on different viewing angles are thus reduced. With pixel electrodes and common electrodes simultaneously disposed on the TFT matrix substrate, this method features larger viewing angle of liquid crystal display. In addition, electrodes are periodically disposed and the electric field parallels the panel.
Lateral electric field mode is suitable for transmissive, reflective and semi-transparent displays. Active driven techniques are well suited for semi-transparent displays, and exhibit advantages of both reflective and transmissive displays, such as amorphous-silicon TFT or low temperature polysilicon TFT. Therefore, current low-consumption IA products typically employ semi-transparent display panels. Electrodes, however, can only be placed on one side of the two substrates and strips of electrodes must be arranged periodically when applying lateral (horizontal) electric field. This is problematic as diffraction indices in periodic electrode arrangements and the surrounding dielectric material are different, thus incident light diffraction occurs. Consequently, the light utilization rate is reduced and stray light within the system further hinders display contrast. For projection systems, in particular, only reflected lights with smaller angles are collected, diffracted lights with greater angles lower the illumination efficiency considerably.